A direct military attack by Russian forces on the United States is, of course, unlikely. But a Russian attack on Moldova is far from unthinkable. It is entirely possible that Putin will attack a NATO member such as Lithuania, Latvia, or even Poland, whose people have gone to such extraordinary lengths to assist the Ukrainians. There are already Americans fighting in Ukraine, as private volunteers rather than as part of our armed forces. If Putin is looking for a pretext, he will have no trouble finding one.

The United States is keenly interested in keeping the fighting in Ukraine. But the fighting will stay in Ukraine for only as long as Putin believes it is in his interest to keep it there. That may not be much longer. Putin already has failed to achieve his main political objective in Ukraine and will not achieve it no matter how long the conflict drags on; what was intended as a show of awesome military might has instead been a display of weakness and incompetence. A wider war — a glorious crusade — might soon suit Putin’s purposes better than does a quagmire in Ukraine, where the Russian army has been reduced to trying to substitute atrocities for victories.

President Joe Biden has said that U.S. forces will defend “every inch” of NATO territory. But Biden was there when the Obama administration offered a lot of big talk about “red lines” in Syria and then did nothing. Biden’s people right now are engaging in counterproductive (to say the least) negotiations with Tehran that serve no obvious U.S. interest, and going through Moscow to do so. Vladimir Putin calculates and, as he has just demonstrated, he sometimes miscalculates. Putin might be inclined to take an inch and put Biden to the test.